In semiconductor manufacture, during the manufacturing process, wafers (disk-like objects) are sequentially processed in a plurality of process steps, wherein a plurality of similar, repetitive structural elements, the so-called dies, are produced on a wafer.
In order to produce the dies, a plurality of photoresist layers must be applied one after the other on the wafer. During processing of the wafer, these applied photoresist layers are removed in a peripheral area. Checking the sufficient and complete removal of these photoresist layers is of considerable importance for the subsequent process steps. Remaining photoresist residues on the periphery of the disk-like object can lead to reduced quality when subsequent layers are applied and when the dies are structured.
The German Patent Application No. DE 103 24 474.3 A1 discloses an apparatus for wafer inspection. An incident-light lighting means having an illumination axis and an imaging means having an imaging axis are provided. The lighting means and the imaging means are inclined with respect to each other and directed towards the surface of a disk-like object. The quality of the peripheral area is determined by means of polarized light, and the image of the peripheral area is recorded by a linear array camera. Detecting complete edge bead removal, however, is not possible with the apparatus shown here.
US Patent Application US 2004/0223141 A1 discloses a detection of edge bead removal by means of reflection. A method and apparatus for improving the image contrast between an area covered with photoresist on the one hand and bare silicon on the other are disclosed. The method and apparatus can be used for inspecting the edge bead removal. Herein the wafer is illuminated separately with vertically polarized light and parallel polarized light in the vicinity of the Brooster angle of silicon or the photoresist. A difference image between the reflected, vertically polarized light and the reflected, parallel polarized light is generated. While the method or apparatus described here may be suitable for checking complete edge bead removal, the method or apparatus is based on a different technological principle from the present invention.
US Patent Application US 2005/0013476 A1 discloses a method of measuring the edge bead removal also comprising the detection of an edge at the circumference of the wafer. The position of the wafer notch at the periphery of the wafer is determined. The position of the wafer center is also determined. Moreover the distance between the wafer edge and the EBR (Edge Bead Removal) line is determined at the wafer circumference. The EBR line is determined from a bright field and a dark field.
From US Patent Application US 2005/0036671 A1, an apparatus for inspecting a periphery or edge of a wafer is known. The inspection device for semiconductor products comprises a camera for recording images of the peripheral area of the top surface of the wafer, a camera for imaging the circumferential surface, normal to the surface of the wafer, and a checking means for receiving the images of the peripheral area of the top surface of the wafer and from the circumferential surface of the wafer. The checking means is for analyzing the images of the peripheral area of the top surface of the wafer and of the circumferential surface of the wafer in order to be able to determine defects thereon.